Which app were you using on Windows 8.1? May i connect with you remotely to check this for you? Thanks
Were you using the mail app on windows 8.1? or windows live mail, thunderbird, etc?
What is the part after the @ symbol of your email address?
Since this is a technical issue, it will need to be troubleshooted, in order to that i need some information from you so i can tell you what to do. What is the part after the @ symbol of your e-mail address?
Okay. Please go here and login to this email address and tell me if you see the older emails on the webmail.
Okay. In the mail app, do the following:Swipe in from the right edge of the screen, and then tap Settings.(If you're using a mouse, point to the upper-right corner of the screen, move the mouse pointer down, and then clickSettings.), Tap or click Accounts, Tap or click the account you want., and adjust the setting for "How far back to go to get messages (from as short as the last three days to any time)." to download older messages.
Did it work?
May i connect with you remotely to do this for you?
I already have, you need to change the sync settings. Do you see account settings?
Do you see a settings wheel in the left pane (bottom)?
select "Change mailbox sync settings". Where it states "Download email from", change it to "Any time".
What options do you see?
Did you click the settings wheel from the left pane?
Let me re-list the steps:At the bottom of the left navigation pane, choose Settings . ( a settings wheel)Choose Accounts, and then choose the account that you want.Choose Change mailbox sync settings.Under Download new content, choose an option as appropriate.Under Download email from, choose any time or another option as appropriate.Choose Done > Save.
You need to be in the Mail app to follow the steps. It appears to me that you went to Windows Settings. Please open Mail App, and then follow the steps below:At the bottom of the left navigation pane, choose Settings . ( a settings wheel)Choose Accounts, and then choose the account that you want.Choose Change mailbox sync settings.Under Download new content, choose an option as appropriate.Under Download email from, choose any time or another option as appropriate.Choose Done > Save.
I can direct you to the Microsoft site, with the same steps. https://support.office.com/en-ie/article/Resolve-sync-issues-in-Mail-and-Calendar-apps-in-Windows-10-0dd86c69-18f3-4f73-9d3d-375bdc9c3e34?ui=en-US&rs=en-IE&ad=IE&fromAR=1
There is nothing else left for me to answer as i already have answered. If you cannot follow these steps, i can remote in and do this for you in less then 2 minutes.
I've just sent you the link, where Microsoft instructs the same for Windows 10 Mail app. If i connect, i'll follow my own steps so you can see that they work.